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Alert Notice 639: CH Cyg coverage requested

Note: CH Cyg recovered in early August from the fading episode described below. However, ongoing coverage is extremely important, with V and particularly B being given priority over Rc and Ic. As always, visual observations are requested and encouraged. - Elizabeth O. Waagen, November 29, 2018

July 3, 2018: The symbiotic variable CH Cyg is undergoing a fade that began on June 25. Multicolor photometry is requested; V and particularly B should take priority over Rc and Ic. Observations made two to three times a week are sufficient; time series observations are not needed. Visual observations are also requested and encouraged. Spectroscopy would be very welcome and appreciated. Coverage should continue throughout the observing season.

The AAVSO has had an ongoing campaign on CH Cyg for Dr. Margarita Karovska (Harvard-Smithosonian Center for Astrophysics) underway for the past several years (links below). These fading events are of particular interest when the system fades most in B, as is currently happening. There is not a long history of B observations of CH Cyg, so it is essential to have good coverage in B throughout the fading episode and afterwards.